The present invention relates to electronic amplifiers. It furthermore relates to audio amplifiers. In particular, the invention relates to an electronic amplifier where non-linearities of an output transducer coupled to the amplifier may be controlled and compensated. Even more particularly, the present invention relates to an amplifier arrangement having a control circuit fed by a servo mechanism disposed on the output transducer coupled to the amplifier, thereby controlling and correcting nonlinearities in the response generated by the output transducer. For example, the present invention has particular application to the control of nonlinearities generated by loudspeakers coupled to audio amplifiers.
Current audio reproduction is achieved through a system of amplification and reproduction in which the amplifier increases both voltage and current levels, while a transducer produces acoustic output by conversion of electrical energy into acoustic energy. Often the transducer, i.e., a loudspeaker, does not follow its input in linear fashion, resulting in phase, frequency, amplitude and harmonic distortion.
U.S. Pat. No. 4,868,870, issued to the present applicant, describes an amplifier system which copes with transducer nonlinearities through detection and correction of these nonlinearities.
However, that patent describes a system having a voltage controlled amplifier which can introduce some distortion characteristic, though small, of its own. The system of the present invention provides a new gain cell for a voltage controlled amplifier which has an extremely low distortion characteristic. The present invention also uses pulse width modulation techniques. Additionally, the present invention seeks to provide an amplifier arrangement which generally reduces distortion to a minimum.